The S400 and the Patriot etc all suffer from the same problem: They only deny the enemy high elevation flight.

Russian doctrine has been based around big, fast things going high. NATO doctrine has been about smaller, slower things going very low. Going low leaves you very vulnerable if you get too close to a defender, but there's no way there are defenders everywhere.

An extreme example of the problem was the Moskova--big, fast missiles that couldn't see something coming in just above wavetop height. There were only two launchers that had any possibility of engaging and only time for one launch cycle--and that probably only if they already had a bird on the rails. (Exposed to the elements, rather than safe in the magazine.)